SALPIDAE FORMS WITH COVERING FOLDS. 



433 



B. Forms with Covering Folds. 



The development of the forms belonging to this type (*5'. (Cyclosalpa) 

 pinnata, ti. africana-niaxima, *S'. wmcinata-fusiformis, $. punctata) 

 differs in many essential points from that of S. dwnocratica-mucronata. 

 The principal distinction consists in the presence in the former of an 

 external covering which after the degeneration of the primary brood - 

 sac (present also in *S'. <lemo<:ratica-mucronata), forms a secondary sac 

 investing the embryo, and in the peculiar development of the placenta. 

 The development of the organs also appears to follow another type.* 

 The forms just mentioned seem to agree fairly well in their develop- 

 ment, which has been studied by many /oologists, especially by 



X 



Ki<;. -217. Two outogenetic stages of Salpa pinnata (after SALKNSKY) forming a 

 sequence to Fig. 210 /*. b, blastomeres ; bk, "blood-forming bud" ; bl, blood- 

 cavities in the placenta ; bl', median blood-sinus ; d, roof of the placenta (basal plate) ; 

 e, lower part of the epithelial prominence, known later as the placental membrane ; 

 >-', upper part of the epithelial prominence (SALENSKY'S ectoderm-germ) ; /, follicular 

 rarity ; ./'//, covering iold ; fiv, follicle-wall. 



TODARO, BARROIS and SALENSKY, and more recently by BROOKS 

 (No. I.), HEIDER (No. XIII.), and KOROTNEFF (Nos. XX., XXa., 

 and XXIa.). The following account relates chiefly to 8. pinnata, a 

 comparatively well-known form. 



Starting with the embryonic development of S. pinnata at the 

 stage depicted in Fig. 217 A, we find conditions in fairly close agree- 

 ment with those described in connection with 6'. democratica. The 

 embryo consists of large and of small cells. The protoplasm of the 

 large cells (b) breaks up in a peculiar way into polygonal portions 



* [See footnote, p. 423 and p. 445. ED.] 

 FF 



